Re: Swapping activated while RAID reconstruction in progress
On Mon, 29 Jan 2001, Michael Bilow wrote:
> Well, if you are getting to the completion of RAID resync, then whatever
> problem you are having is not the one that I was reporting in those bugs.
> At the time, the behavior if swapping was started during the RAID resync
> was a hard system crash with a kernel panic. In no case did this ever
> result in actual corruption of the data on the filesystem being resynced,
> but that is certainly a possibility. The bugs I reported really were
> fixed in the Potato release.
Sorry, for the delay in replying. Your mail hit the nail on the head. I
now agree that the problem I saw was not related to the bug-report you had
filed.
The md0 was OK, it was the ext2fs on the device that was corrupt, badly.
> The main exception to this clean interface is that, in emergencies, the
> filesystem tools such as e2fsck can be used as a last resort against the
> component partitions with RAID totally disabled. This is not the proper
> way to recover a broken RAID set, and the raidtools2 utilities should be
> used for that. However, if something catastrophic were to happen with the
> RAID utilities themselves or the kernel RAID code, provision has been made
> for accessing the component partitions directly. This was done through
> the simple expedient of putting the RAID-specific information -- the
> "persistent superblocks" -- at the end of the component partitions instead
> of at the beginning, so that the first 99.999% or so of each component
> partition looks to e2fsck as if it has a meaningful ext2 superblock at the
> beginning.
Yes!!! Added another disk, installed a basic Debian on it, and started
trying to find the ext2fs on /dev/hda2 (not /dev/md0). Took quite some
time finding a superblock that was usable, but it finally worked. Checked
that the data was OK (mostly mail spools), and then backed up, recreated
ext2fs on /dev/md0, restored, booted, and WOW!
> Note that I am not actually advising you to access the data
> this way, but simply advising you of the possibility should all else fail.
> (This is also done to allow booting from a RAID component, since clearly
> the ROM BIOS has no knowledge of Linux software RAID and Lilo has to get
> files loaded within that constraint.)
I understand your advice, but I was desperate, and understand ext2 better
than RAID.
> There are some extensive discussions of all of this in the RAID HOWTO --
> http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/ -- and most of what you
> are dealing with is not Debian-specific. As a result, you might be more
> likely to get help with a serious problem on the Linux-RAID mailing list.
True, but the problem was my wrong diagnosis of the issue, thinking it to
be a debian-specific bug. The error I got, (swapper uses obsolete iocts,
followed by a panic), seemed to fit your report.
Once more, my heartfelt thanks to your support.
--
Sanjeev "ghane" Gupta Mob: +65 98551208
dotXtra Pte Ltd Fax: +65 2275776
Singapore email: ghane@dotxtra.com
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